Gamma rays from giant-molecular clouds

An examination of the evidence favouring the detection of gamma rays from the irradiation of giant molecular clouds by cosmic rays is given. Data relevant to specific nearby clouds are studied in some detail and the evidence favouring some of the so-called gamma ray sources being due to the irradiation of these and more distant clouds is critically assessed. The need for enhancement of cosmic ray intensity in some clouds is discussed. The relevance of this work to interpretation of current and planned X-ray measurements as well as future gamma-ray space missions is discussed.     

Gamma rays and cosmic ray gradiants

The advent of data from the Gamma Ray Observatory, of much higher precision than hitherto, will open up the possibility of deriving more precise results on the presence of ‘cosmic ray gradients’ in the Galaxy. There will still be a variety of difficulties, however. There are still uncertainties in the mass of gas in each of its major forms, HI, H₂ and HII, and their corresponding spatial distribution and the photon field in the Galaxy are known imprecisely. The problem of the contribution to the gamma ray flux from unresolved discrete sources will still be present, too, albeit at a lower level than previously. The division of parent particles between electrons and protons (nuclei) will also continue to be rather uncertain.

These problems are examined in the paper.     

Puzzles of the cosmic ray anisotropy

We discuss three of the known puzzles of the cosmic ray anisotropy in the PeV and sub-PeV energy region. They are (1) the so called inverse anisotropy, (2) the irregularity in the energy dependence of the amplitude and phase of the first harmonic and (3) the contribution of the single source.